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chapter 22

microevolution

evolution within a population

macroevolution

evolutionary change above a species level

the biological species concept

a species is a group of populations whose individuals can interbreed and produce viable, fertile offspring

who developed the biological species concept

ernst mayr

gene flow between populations does what

holds the phenotype of a population together

reproductive isolation

the existence of biological factors that impede two species from reproducing viable fertile offspring

prezygotic barrier

prevent fertilization

postzygotic barriers

prevent viable and fertile offspring after fertilization

habitat isolation

a type of reproductive isolation
two species encounter eachother so infrequently because they inhabit different habitats even though there is no physical barrier between them

temporal isolation

species that breed at different times cannot mix gametes
prezygotic barrier

behavioral isolation

courtship rituals and other behaviours unique to a species prevent mating
prezygotic barrier

mechanical isolation

morphological differences prevent successful mating
prezygotic

gametic isolation

incompatible gametes prevent fertilization
prezygotic

reduced hybrid variability

offspring is infertile
postzygotic barrier

hybrid breakdown

2nd generation is infertile
postzygotic barrier

limitations of the biological species concept

doesn't apply to fossils or asexual organisms

the morphological species concept

morphological similarities make a species

ecological species concept

views species in terms of its ecological niche

phylogenetic species concept

species defined by the smallest group of individuals on a phylogenetic tree

2 main types of speciation

sympatric allopatric

allopatric speciation

gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

sympatric speciation

speciation takes place in geographically overlapping populations

polyploidy

there are an extra set of chromosomes due to a mistake in cell division

autoploidy

an individual has more than 2 chromosome sets derived from one species

alloploidy

an individual has more than two sets of chromosomes derived from different species

why cant a new polyploid individual breed with its ancestors?

because of the chromosomal mismatch

animals are generally unsuccessful reproducing tetraploid generations because

the new generation has no one to mate with because of the mismatch in chromosomal compliment

plants are successfull in producing tetraploid individuals because

they can asexually reproduce more mates for the 4n individuals

hybrid zone

a region in which members of different species mix and mate, producing at least some offspring of mixed ancestry

reinforcement

hybrids are less fit than members of their parent species, so natural selection strengthens prezygotic barriers to reproduction

fusion

barriers to reproduction may be weak when two species meet in a hybrid zone
so much gene flow occurs so the species fuse together

stability

many hybrid zones are stable in that hybrids continue to be produced

how long does speciation take

can be fast or over thousands of years

punctuated equilibria

Niles Eldredge and stephen jay gould coined the term
describes periods of apparent equilibrium punctuated by a sudden change

contrasts model of gradual change

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